[BUG] Model Identity Mismatch in Claude Code

Environment

• Platform (select one):
• [ ] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [x] Other: Claude Code (claude.ai/code)
• Claude CLI version: 1.0.69 (Claude Code)
• Operating System: macOS (Darwin 23.1.0)
• Terminal: iTerm2 Build 3.5.11

## Bug Description
When selecting "Opus" model via /model command in Claude Code, the system continues to use Sonnet 3.5 instead of the selected model. This is a critical issue as users are
not getting the model they explicitly chose.

## Steps to Reproduce

1. Open Claude Code at claude.ai/code
2. Run /model command
3. Select "opus" from the options
4. System responds with "Kept model as opus"
5. Check actual model being used - it's claude-3-5-sonnet-20241022 not Opus

## Expected Behavior

• When selecting "Opus" via /model command, the system should actually switch to and use an Opus model
• The model selection should be honored and reflected in actual operation
• Users should get the performance and capabilities of the model they selected

## Actual Behavior

• /model command shows "Kept model as opus"
• System prompt claims "You are powered by the model named Opus 4.1"
• But the actual model running is claude-3-5-sonnet-20241022 (Sonnet 3.5)
• User's model selection is completely ignored